std::is_copy_constructible, std::is_trivially_copy_constructible, std::is_nothrow_copy_constructible
From Cppreference
| Defined in header <type_traits>
| ||
| template< class T >
struct is_copy_constructible; | (1) | (since C++11) |
| template< class T >
struct is_trivially_copy_constructible; | (2) | (since C++11) |
| template< class T >
struct is_nothrow_copy_constructible; | (3) | (since C++11) |
1) If the constructor expression T(arg); is well-formed for arg of type const T& (that is, T is a scalar or reference or a class with an accessible copy constructor), provides the member constant value equal true. For any other type, value is false.
2) same as 1), but the copy constructor expression does not call any operation that is not trivial.
3) same as 1), but the copy constructor expression is noexcept.
Contents |
Inherited from std::integral_constant
Member constants
| value [static] | true if T is copy-constructible , false otherwise (public static member constant) |
Member functions
| operator bool | converts the object to bool, returns value (public member function) |
Member types
| Type | Definition |
| value_type | bool |
| type | std::integral_constant<bool, value> |
[edit] Equivalent definition
template<class T> struct is_copy_constructible : std::is_constructible<T, const typename std::add_lvalue_reference<T>::type> {}; template<class T> struct is_trivially_copy_constructible : std::is_trivially_constructible<T, const typename std::add_lvalue_reference<T>::type> {}; template<class T> struct is_nothrow_copy_constructible : std::is_nothrow_constructible<T, const typename std::add_lvalue_reference<T>::type> {}; |
[edit] Example
#include <iostream> #include <type_traits> struct Ex1 { std::string str; // member has a non-trivial copy ctor }; struct Ex2 { int n; Ex2(const Ex2&) = default; // trivial and non-throwing }; int main() { std::cout << std::boolalpha << "Ex1 is copy-constructible? " << std::is_copy_constructible<Ex1>::value << '\n' << "Ex1 is trivially copy-constructible? " << std::is_trivially_copy_constructible<Ex1>::value << '\n' << "Ex2 is trivially copy-constructible? " << std::is_trivially_copy_constructible<Ex2>::value << '\n' << "Ex2 is nothrow copy-constructible? " << std::is_nothrow_copy_constructible<Ex2>::value << '\n'; }
Output:
Ex1 is copy-constructible? true Ex1 is trivially copy-constructible? false Ex2 is trivially copy-constructible? true Ex2 is nothrow copy-constructible? true
[edit] See also
| (C++11) (C++11) (C++11) | checks if a type has a constructor for specific arguments (class template) |
| checks if a type has a default constructor (class template) | |
| (C++11) (C++11) (C++11) | checks if a type has a move constructor (class template) |
